1. Field of the Invention
The present invention relates to a coordinate inputting/detecting apparatus, and more particularly relates to an optical touch panel type coordinate inputting/detecting apparatus, that is integrated and used with an electronic white board or a large display apparatus, or used in conjunction with a personal computer, and that optically detects a coordinate position designated by a designating member, such as a pen, or a finger, for inputting or selecting information represented by the coordinate position designated by the designating member.
2. Discussion of the Background
A coordinate inputting/detecting apparatus is known in which, when a coordinate inputting surface of the coordinate inputting/detecting apparatus is pressed by a pen or when the pen approaches the coordinate inputting surface, an electrical change is caused by an electrostatic charge or an electromagnetic induction, and thereby the coordinate position of a point pressed or approached by the pen is detected.
Also, a touch panel type coordinate inputting/detecting apparatus using an ultrasonic wave is known in which, when a panel is touched, a surface elastic wave emitted over the panel is attenuated and thereby a touched position on the panel is detected, as described, for example, in Japanese Patent Laid-open Publication No. 61-239322.
However, in such a coordinate inputting/detecting apparatus that detects a coordinate position using an electrostatic force or an electromagnetic induction, an electrical switching function must be provided at a coordinate inputting surface of the coordinate inputting/detecting apparatus, thus increasing the manufacturing cost of the apparatus. Further, the pen must be connected to a main body of the apparatus, for example by a cable, which makes the operation relatively difficult.
Further, a coordinate inputting/detecting apparatus using an ultrasonic wave is generally configured for a finger to be used as a designating device. When a pen made of soft elastic material is used for the designating device, in writing a straight line with the pen on a panel, for example, although the attenuation of a surface elastic wave is reliably obtained when the pen is pressed against the panel, a sufficient contact of the pen with the panel is not obtained when the pen is moved, and thereby the line is broken. On the other hand, if the pen is pressed unnecessarily strongly while moving the pen for obtaining the sufficient contact with the panel, as the pen is moved, the panel receives a stress from the pen because of the elasticity of the pen. This causes a distortion in the panel, and a reverting force is exerted while the pen is moved. Therefore, in writing a curved line with the pen, the force of pressing the pen decreases such that the reverting force is greater than the pressing force. As a result, the attenuation of the surface elastic wave is not reliably obtained and thereby it is determined that the input is discontinued. Thus, the coordinate inputting/detecting apparatus using an ultrasonic wave has a problem in obtaining a high reliability of inputting when a pen is used for a designating device.
Further, various attempts have been made to solve the drawbacks of the above-described coordinate inputting/detecting apparatuses by providing optical type coordinate inputting/detecting apparatuses as described, for example, in Japanese Patent Laid-open publications No. 5-173699 and No. 9-319501. A touch panel type coordinate inputting/detecting apparatus having a relatively simple construction can be realized using such an optical type coordinate inputting/detecting apparatus.
Optical type coordinate inputting/detecting apparatuses have recently been widely used in conjunction with a personal computer as an effective tool for inputting or selecting information in the personal computer. However, unlike a coordinate inputting/detecting apparatus using an ultrasonic wave, a coordinate inputting/detecting surface (i.e., a touch panel) of such optical type coordinate inputting apparatuses does not have a detecting function by itself, and an optical detecting area is provided at a position slightly apart from the coordinate inputting/detecting surface of the coordinate inputting/detecting apparatus. Therefore, a space deviation exists between the actual plane where, for example, an image (e.g., character) is drawn (written) with a finger, i.e., the coordinate inputting/detecting surface, and a plane where the coordinates of the drawn image (character) are detected, and contrary to the intention of a person drawing the image (character), a trail is caused on the drawn image (character), that is reproduced, for example, on a display. That is, in an optical type coordinate inputting/detecting apparatus, a leaving of a finger from the touch panel is detected not in an instance when the finger separates from the touch panel but when the finger separates from the touch panel by more than a certain distance. Therefore, before the finger reaches such a certain distance separated from the touch panel and where the finger is actually detected as separated from the touch panel, although an operator has already intended his/her finger to be separated from the touch panel surface and drawing of a desired character has been already completed, the finger is still detected as touching the touch panel (as being inserted in the coordinate inputting/detecting area). Thereby, an unintended line is drawn at a part of a reproduced image. Such a phenomenon of drawing an intended line is called a trailing phenomenon.
For example, as illustrated in FIG. 20, when a coordinate inputting/detecting area 200 is provided at a surface side of a touch panel 201, and if a finger 202 draws a line along the surface of the touch panel 201 and separates from the surface of the touch panel 201 upon ending the drawing at a point P, the finger 202 is continued to be detected by a detecting light as touching the touch panel 202 until reaching a point P′ where the finger 202 leaves the coordinate inputting/detecting area 200. Thus, the finger 202 is first detected as separated from the touch panel 202 at the point P′. Accordingly, a drawing line 203 which is displayed at a surface of the touch panel 201 via a display device does not end at the point P but instead extends to the point P′, and the part between the points P and P′ is displayed as a trailing line 204. In practical drawing cases, for example in drawing a Japanese Kanji character corresponding to 2 (two) as illustrated in FIG. 21A, a line is first drawn from a point {circle around (1)} to a point {circle around (2)}, and then the finger is separated from the touch panel 202 at the point {circle around (2)}. Thereafter, another line is drawn from a point {circle around (3)} to a point {circle around (4)}, and the finger is separated from the touch panel 201 at a point {circle around (4)}. In actual drawing, however, when separating the finger from the touch panel 201 at each ending portion 205 of the points {circle around (2)} and {circle around (4)}, the above-described trailing phenomenon occurs, such that a trailing line portion 204 like a whisker is generated at each ending portion 205 as illustrated in FIG. 21B, thereby deteriorating the visibility of the drawn character. Therefore, after the drawing is completed, a troublesome operation, such as erasing the trailing line portion 204 by manipulating an erasing tool, is necessary.
Further, some Japanese Kanji and Hiragana characters have a sweeping up portion, such as, for example, a sweeping up portion 206 of Japanese Kanji character “sun” as illustrated in FIG. 21C, and a sweeping portion, such as, for example, a sweeping portion 207 of Japanese Hiragana character “tsu” as illustrated in FIG. 21E. Because these sweeping up and sweeping portions are requisite drawings in Japanese Kanji and Hiragana characters, it is necessary to distinguish these sweeping up and sweeping portions from a trailing line portion in the stopping portion 205. FIGS. 21D and 21F illustrate examples of reproduced drawn Kanji character “sun” and Hiragana character “tsu”. As illustrated, a trailing line portion 204 may be generated at each of the stopping portions 205 and tip ends of the sweeping up portion 206 and the sweeping portion 207.
Thus, the above-described trailing problem in the optical type coordinate inputting/detecting apparatus is caused by a fact that a deviation exists between the actual designating condition of a designating member, such a finger, and the determination or the recognition of the designating device in the coordinate inputting area of the coordinate inputting/detecting apparatus. The result of which is that determination as to whether the designating device is inserted in the coordinate inputting/detecting area or recognition of the designating member in the coordinate inputting/detecting area of the coordinate inputting/detecting apparatus is not reliably made.
Further, the touch type coordinate inputting/detecting apparatus must be configured to include an optical unit to optically detect a designating device such as a finger or a designating member. Therefore, even when a surface of a coordinate inputting/detecting area (a touch panel) is touched by a same designating device, depending upon the position where the designating device touches the coordinate inputting/detecting area surface, the quantity of a light received by a light receiving portion of the optical unit changes. That is, the quantity of the light received by the optical unit decreases as the position where the designating device touches the coordinate inputting/detecting surface moves further from the optical unit.
In the touch panel type coordinate inputting/detecting apparatus as described above, a designating device is determined as being inserted in an optical detecting area, that is provided at a position slightly separated from a coordinate inputting/detecting surface of the coordinate inputting/detecting apparatus, when a signal, that is obtained when the designating device is inserted in the optical detecting area, exceeds a threshold value. In this case, if the threshold value is set too high, the designating device fails to be detected as being inserted in the detecting area even when the designating device is inserted in the detecting area, and on the contrary, if the threshold value is too low, the above-described trailing phenomenon is remarkable. Namely, the threshold value causes a trade-off relation between the detecting capability and the occurrence of a trailing phenomenon.
The threshold value further relates to a distance between the optical unit and the designating device. That is, if the threshold value is too high, at a position far from the optical unit, the designating device can not be determined as being inserted in the detecting area even when the designating device is inserted in the detecting area. On the contrary, if the threshold value is too low, at a position near the optical unit, a trailing phenomenon is caused. Thus, setting of an optimum threshold value is difficult.